1. Field of the Invention
The present invention relates to a semiconductor device having a trench interconnection to prevent diffusion of ions and the like between layers and a method of forming a barrier film for a semiconductor device. More particularly, the present invention relates to a barrier film capable of preventing increase in an interconnect resistance caused by heat treatment in the course of fabrication of the device.
2. Description of the Related Art
Recently, a trend of higher integration of elements in a semiconductor device has been advanced in accordance with miniaturization of its size. Accordingly, in a conventional semiconductor device, a size of a contact hole and a line width in interconnection have been smaller, but an aspect ratio (a quotient of a height or depth divided by a width) has been larger, since a dimension in a direction of the thickness of a substrate has not been smaller. In the case of 256 Mb DRAM, an aspect ratio of a contact hole is 4 or more. As for a method of forming interconnection, a damascene method has been used in many cases. The damascene method is to form a trench in an insulating film, and thereafter to fabricate an interconnect by filling the trench with a metal, and the method draws keen attention as a method of fabricating a copper interconnect, which has difficulty in fine etching.
Conventionally, as fabricating method of barrier films for a contact hole and a trench, it has been common to deposit a TiN film by means of a sputtering method. When an aspect ratio is larger, however, a film cannot be deposited on the side and bottom surfaces of the contact hole or the trench even with employment of a sputtering method. Therefore, a chemical vapor deposition method (CVD method) has recently come to be employed.
A method of fabricating a metal compound thin film, such as a WNx film and a WSix film is disclosed in, for example, Publication of Unexamined Japanese Patent Application No. Sho 63-317676. In the publication, it is described that the WNx film has a non-granular structure. A method of fabricating a semiconductor device has the step of forming a WNx film by giving a nitrogen plasma treatment on a substrate in the course of deposition of a tungsten film. These are methods of fabricating WNx film better as a barrier than a W film.
As described above, a conventional WNx film has an advantage that the WNx film exhibits better performance as a barrier than the W film. However, it is well known that the WNx film is crystallized from its original amorphous structure at about 700xc2x0 C. and nitrogen is dissociated from W in a bond of Wxe2x80x94N at 850xc2x0 C. Therefore, if the WNx film is employed as a barrier film, a property as a barrier may be deteriorated through a structural change of the film, depending on fabrication conditions of a semiconductor device.
A method of fabricating a W film on a substrate with ease is disclosed in Publication of Unexamined Japanese Patent Application No. Hei 6-291067. FIG. 1 is a typical view showing a conventional apparatus of fabricating a W film. In FIG. 1, a substrate holder 2 is disposed in a CVD chamber 1 and an electrode 26 is arranged above the substrate holder 2. The substrate holder 2 and electrode 26 are connected with a high frequency electric source 27 placed outside the CVD chamber 1. A gas in the CVD chamber 1 is discharged by a pump 4 through a discharge port 1a. Gas supply ports 1b, 1c are provided to the CVD chamber 1 and the gas supply port 1b is connected with a WF6 gas bomb 5 through a mass flow controller 8 and the gas supply port 1c is connected with a nitrogen gas bomb 21 through a mass flow controller 8.
In the case where a W film is formed on a substrate with use of the CVD apparatus as constructed in such a manner, after a substrate 3 is placed on the substrate holder 2, the CVD chamber 1 is evacuated by means of the pump 4. Then, a nitrogen gas and a WF6 gas are supplied into the CVD chamber 1, while flow rates are controlled by the mass flow controller 8 and simultaneously, a voltage is applied between the electrode 26 and substrate holder 2 by means of the high frequency electric source 27. In this condition, a plasma 28 is produced between the substrate 3 and the electrode 26, and the surface of the substrate 3 is charged by free electrons in the plasma. The free electrons work as a catalyst to form a W film on the substrate 3.
With use of a method shown in FIG. 1, since a plasma CVD method is adopted, a reaction in a gas phase becomes active and a W film can be formed on the substrate with no use of SiH4 gas.
However, in the case where the above mentioned plasma CVD method is used to form a W film, products produced in a gas phase are deposited on the periphery of a substrate and thus in general a coverability of a W film on the substrate is reduced and it becomes hard to deposit a barrier film on the inner surfaces of a contact hole and a trench with high aspect ratios in a uniform manner, as in the case of employment of a sputtering method.
When a barrier film is formed, the barrier having a higher resistivity, compared with a W film, a Cu film or the like as interconnection, there arises a problem that a interconnect resistance is increased, since cross-sectional areas of a contact hole and an interconnect are decreased if a thickness of the barrier film is thick. For example, a device having a size of 0.25 xcexcm or less requires that a thickness of a film is about 20 nm or less. Therefore, there is a demand for proposal for a semiconductor device having a trench interconnection and a method of forming a barrier film for a semiconductor device and fabricating method thereof, not only thinner compared with a conventional practice, but also better in coverability.
It is an object of the present invention to provide a semiconductor device having a trench interconnection and method of forming a barrier film with a thin thickness inside a fine contact hole, a fine interconnect trench or the like, thereby increase in a resistance of interconnects formed inside the contact hole or the interconnect trench can prevented and the barrier film has a high-temperature stability.
A semiconductor device having a trench interconnection according to the present invention comprises a semiconductor substrate, an insulating film having a trench formed on the substrate, a barrier film formed on an inner surface of the trench and a conductive material filled into the trench to form an interconnect line. The barrier film is made of material of one kind selected from the group consisting of WSixNy and WCxNy.
A depth of the trench may be smaller than a thickness of the insulating film or so large as to reach the substrate. The conductive material can be Cu, and a Ti film may be formed between the insulating film and the barrier film.
A method of fabricating a semiconductor device according to the present invention comprises the step of forming a barrier film made of material of one kind selected from the group consisting of WSixNy and WCxNy on a semiconductor substrate by causing a reaction among a raw material gas containing W, one kind of gas selected from the group consisting of silane, dichlorosilane and a hydrocarbon gas, and a nitrogen supply source.
The nitrogen supply source can be at least one kind selected from the group consisting of a nitriding plasma, a NH3 plasma, nitrogen gas, NH3 gas, hydrazine and dimethyl hydrazine. The hydrocarbon gas can be a gas of one kind selected from the group consisting of methane gas, ethane gas and propane gas. The gas containing W can be a gas of one kind selected from the group consisting of WF6 gas, W(N(CH3)2)6 and W(N(C2H5)2)6.
A method of fabricating a semiconductor device according to the present invention may further comprise the steps of forming an insulating film on the semiconductor substrate and subsequently forming a trench in the insulating film. The trench has an inner surface where the barrier film should be formed.
Next, a conductive material is used to fill in the trench after the step of forming the barrier film on the inner surface of the trench. A step of filling the trench with a conductive material may be inserted after the step of forming the barrier film.
The nitrogen supply source can be a plasma of one kind selected from the group consisting a nitrogen plasma and an ammonia plasma, and the step of forming the barrier film has the steps of producing the nitrogen supply source and supplying the nitrogen supply source to the surface of the substrate.
Another method of fabricating a semiconductor device comprises the step of causing a reaction between a raw material gas of one kind selected from the group consisting of W(N(CH3) )6 and W(N(C2H5))6 and a gas of one kind selected from the group consisting of SiH4 and SiH4 to form a barrier film made of material of one kind selected from the group of WSixNy and WCxNy.
In the present invention, a barrier film made of WSixNy or WCxNy is formed between either the insulating film and conductive material or the substrate and conductive material. Since crystallization of these films is disturbed in the presence of Si or C, they are more stable even in a high temperature range equal to or higher than 700xc2x0 C., compared with a conventional barrier film made of WNx. Therefore, even if a heat treatment at a temperature of 700xc2x0 C. or higher is performed after formation of the barrier film; no diffusion arises and thus a property as a good barrier can be maintained, so that a semiconductor device having good characteristics can be obtained.
If a barrier film is formed on the substrate under a condition that a reaction of raw materials in a vapor phase, which is a cause for deterioration in coverability, is suppressed and a surface reaction, wherein a reaction of SiH4, CH4 or the like is performed on the substrate, is a rate-determining process, the barrier film having an amorphous phase made of WSixNy or WCxNy can be deposited with a good coverability.
Furthermore, if a step of producing a plasma and a step of supplying the plasma on the surface of a substrate are provided separately from each other, a reaction of a raw material in a gas phase is suppressed and thus a coverability is improved compared with that of a conventional CVD method.
As described above, in the present invention, since a thin film such as of a thickness of 20 nm or less can be formed with a good coverability, compared with a conventional plasma CVD or conventional sputtering method, for example, not only can copper interconnection be adopted, but transmission through interconnection can also be conducted at a high speed with other merits, which makes it possible to improve performances of LSI.